The goal of this research is to gain an understanding of the allosteric regulation of enzyme activity specifically in ribotide reductase from Lactobacillus leichmannii and UDP-glucose dehydrogenase from bovine liver. The presumed reaction course in the former enzyme involves the reduction of an enzyme disulfide bridge in the catalytic center. The rates of reduction of this key disulfide bond and of adduct formation of the two resulting sulfhydryl groups with NEM will be investigated. In particular the influence of effectors, deoxynucleoside triphosphates, on the rate of reaction with NEM will be examined in attempts to demonstrate effector site influences on catalytic site events. Equilibrium binding studies will be carried out with UDPG- dehydrogenase in which substrate, UDPG, and effector, UDPX, will be mutually present. The effects that each of these have on the binding of the other will enable one to differentiate between strict competition for a common binding site and true effector site-catalytic site interactions. The effect of NEM addition to this enzyme will also be investigated. Protection against NEM addition by UDPG and/or UDPX might allow for the preparation of NEM labeled enzymes that are catalytically functional but not regulated by UDPX or vice versa.